1. Field of the Invention
The present invention relates to a plasma processing chamber, a potential controlling apparatus, a potential controlling method, a program for implementing the method, and a storage medium storing the program, and in particular relates to a plasma processing chamber having therein a component element that is exposed to plasma.
2. Description of the Related Art
Plasma processing chambers having a cylindrical vessel, and electrodes that are disposed in the vessel and are connected to radio frequency power sources have been known from hitherto. In such a plasma processing chamber, a processing gas is introduced into the vessel, and the electrodes apply radio frequency electrical power into a space in the vessel. A semiconductor wafer is housed in the vessel as a substrate, and in this state the introduced processing gas is turned into plasma by the radio frequency electrical power, whereby ions and so on are produced, and the semiconductor wafer is subjected to plasma processing such as etching through the ions and so on.
In such a plasma processing chamber, in the case that a mixed gas of a reactive gas such as C4F8 gas and argon (Ar) gas is used as the processing gas, neutral active species (radicals) produced from the reactive gas become attached as a polymer to an inner side wall (hereinafter referred to merely as the “side wall”) of the vessel. If the amount of polymer attached is too high, then when a semiconductor wafer is subjected to the plasma processing, polymer may peel away from the side wall and become attached to a surface of the semiconductor wafer as deposit; it is thus necessary to remove polymer attached to the side wall.
Polymer attached to the side wall is preferably removed by making cations produced when the processing gas is turned into the plasma collide with the side wall. The number of cations colliding with the side wall is affected by the potential of the side wall. Specifically, if the potential of the side wall is low and the potential difference between the side wall and the space in which the plasma is formed from the processing gas is high, then the number of cations colliding with the side wall is increased, and hence the amount of polymer attached is reduced.
However, the potential of the side wall is determined by the anode/cathode ratio which is affected by the electrode shape and the side wall shape, and the magnitude of the radio frequency electrical power which is set so as to obtain desired plasma processing results on the semiconductor wafers. Controlling the potential of the side wall is thus difficult. Controlling polymer removal is thus not easy, and hence if a depositing process for which polymer is readily attached to the side wall and thus deposit is readily attached to the semiconductor wafer surface is carried out repeatedly, then the amount of polymer attached becomes excessive, and hence the frequency of cleaning the side wall must be increased; as a result, the plasma processing chamber utilization ratio decreases.
In recent years, processing chambers have thus been developed according to which the potential of the side wall is actively controlled so as to remove polymer from the side wall, for example a processing chamber according to which once the operating time has reached a predetermined value, the side wall is selectively connected to ground or a radio frequency power source, the side wall being connected to the radio frequency power source and the potential of the side wall being set to a negative potential when removing polymer that has become attached to the side wall, whereby cations are made to collide with the side wall so as to remove polymer from the side wall (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H01-231322).
However, for the processing chamber according to Japanese Laid-open Patent Publication (Kokai) No. H01-231322, in addition to the radio frequency power sources for the electrodes, a radio frequency power source for the side wall, i.e. a radio frequency power source for a processing chamber component element other than the electrodes, is required. There is thus a problem that the construction of the processing chamber becomes complex.
Moreover, for the processing chamber according to Japanese Laid-open Patent Publication (Kokai) No. H01-231322, the radio frequency power source is connected to the side wall so as to remove polymer from the side wall only once the operating time has reached a predetermined value. Controlling the amount of attached polymer is thus difficult, and as a result in the case that a depositing process as described above, and a deposit-less process for which neutral active species are not produced and hence there is no attachment of polymer to the side wall and thus no attachment of deposit to the semiconductor wafer surface such as a process using O2 gas as the processing gas are carried out repeatedly in a single plasma processing chamber, then if the polymer is completely removed from the side wall, the cations will collide not with the polymer but rather directly with the side wall, and hence the side wall will be worn away. As a result, there will again be a problem of the plasma processing chamber utilization ratio decreasing.